Modern Physics Letters A

We describe a dynamical worldsheet origin for the Lagrangian describing the low-energy dynamics of a system of parallel D-branes. We show how matrix-valued collective coordinate fields for the D-branes naturally arise as couplings of a worldsheet σ-model, and that the quantum dynamics require that these couplings be mutually noncommutative. We show that the low-energy effective action for the σ-model couplings describes the propagation of an open string in the background of the multiple D-brane configuration, in which all string interactions between the constituent branes are integrated out and the genus expansion is taken into account, with a matrix-valued coupling. The effective field theory is governed by the non-Abelian Born–Infeld target space action which leads to the standard one for D-brane field theory.

We show that the assumption of quasiperiodic boundary conditions (those that interpolate continuously periodic and antiperiodic conditions) in order to compute partition functions of relativistic particles in 2+1 space–time can be related with anyonic physics. In particular, in the low temperature limit, our result leads to the well-known second virial coefficient for anyons. Besides, we also obtain the high temperature limit as well as the full temperature dependence of this coefficient.

We discuss a realization of stress–tensor for parafermion theories following a construction for higher level affine algebras, based on the projection of the standard level-one bosonic realization on the winding subalgebra. All the fields are obtained from rank free bosons compactified on torus, d. This gives an alternative realization of Virasoro algebra in terms of a nonlocal correction of a free field construction which does not fit the usual background charge of the Feigin–Fuchs approach.

We analyze the problem of the Nielsen–Olesen unstable modes in the SU(2) lattice gauge theory by means of a recently introduced gauge-invariant effective action. We perform numerical simulations in the case of a constant Abelian chromomagnetic field. We find that for lattice sizes above a certain critical length, the density of effective action shows a behavior compatible with the presence of the unstable modes. We put out a possible relation between the dynamics of the unstable modes and the confinement.

The conversion of photons into axions in a periodic external electromagnetic field, i.e. the TE_m0 mode, is considered in details by using Feynman methods. The differential cross-sections are given. It is shown that the lowest mode gives the main contribution to the considered process.

In this letter, we introduce a new statistics to describe particles whose creation and annihilation operators satisfy the relation aa^†-qa^†a=1 in the case of q^s+1=1.

We investigate two-parameter deformed Weyl–Heisenberg algebra in the Fock–Bargmann representation. The commutator [a_qp,ā_qp] acts like squeezing operator on the space of the entire analytic functions. We find that the second parameter gets absorbed into the first parameter, yielding the same result for squeezing as in the case of single parameter study.

We investigate a model of SU(2) ⊗ U(1) singlet scalars coupled to Standard Model. We point out that for the case of the maximal mixing between singlet scalars and the standard Higgs boson, the Higgs boson production cross-section is smaller than the standard Higgs boson production by a factor of 1/(N+1), where N is the number of singlet scalars. For the case of large mixing, Higgs boson could be unobservable at LHC. However, there is also the possibility for the observation of scalar singlets at LHC. As a semi-realistic example, we discuss supersymmetric SU(2) ⊗ U(1) electroweak model with an additional singlet chiral superfield.

Using the ζ-function regularization method, we compute expressions for the bosonic and fermionic partition functions for a field theory defined on a sphere S³. We also analyze their behavior with the radius r₀ of this manifold, showing that for specific values of the field's masses closed expressions can be obtained, which give a completely different behavior as r₀→∞, indicating isolated discontinuities of these partition functions with the masses of the matter fields.